In the scientific study of small streams and rivers, it is desirable to take accurate readings of the various hydrological parameters of the stream, particularly those involving river flow. In order to measure flow velocity, a variety of current flow meter devices have been developed specifically which test the current at desired levels underwater. In U.S. Pat. No. 1,034,399 (Buck) there is disclosed a current meter for measuring the velocity of air or a liquid which comprises a rod, a base, and fluid pressure chambers connected to tubes for receiving fluid and gauging fluid velocity. U.S. Pat. No. 1,862,935 (Langley) discloses a current meter which comprises a meter rod having stabilizers which can be supported by a pulley system and attachable to a boat station. Still other devices disclosed in the prior art include U.S. Pat. No. 1,593,291 (Critchlow) which discloses a flow meter having a velocity wheel suspendable in a fluid, and U.S. Pat. No. 4,122,714 (Kobayashi et al.) wherein a magnetic current meter is adapted to sense the flow of liquid through an open channel.
It is most preferable to measure flow velocity in a small stream or river by wading into the river and taking width, depth and velocity measurements with a hand-held rod having a current meter attached thereto. The current meter on this rod should be adjustable to any wadable depth so that the observation position of the current meter can be set. This rod should transmit the signal from the attached current meter internally to a read-out device which, preferably, also mounts on this rod in a manner that makes the read-out device easy to see and to operate. At present, the most commonly used wading rod for this purpose is known as a top-setting English wading rod (such as described in Buchanan et al., "Discharge Measurements at Gaging Stations", Techniques of Water Resources Investigations, U.S. Geological Survey, Book 3, Chapter 48, 1969, pp. 9-11) which is composed of metal parts and has external rod wires connecting a current meter to a signal receiving device, usually a telephone operator's headset. The device is operated by placing the rod so that the current meter is situated in the flowing stream while the hydrographer listens for clicks in the telephone operator's headset which will correspond to the revolutions of a bucket wheel which rotates within the yoke of the current meter. A determination of velocity is made depending on the number of clicks or revolutions of the bucket-wheel received over a measured period of time as determined using a stopwatch.
The use of the top-setting English wading rod encounters several major drawbacks, however, which can lead to inaccuracies in the velocity readings or make the flow readings difficult or impossible to obtain. In particular, the English rod has a low degree of noise rejection in streams with high specific electrical conductance. As a result, when the conductance in a stream is higher than normal, the English rods will not work with newly developed electronic read out devices such as a current meter digitize (or CMD). Additionally, the hex and round rods of the English Wading Rod are part of the electrical circuitry for this equipment, and thus expose a considerable surface area of the path of the electrical circuit to the fluid in which the equipment is immersed. If this fluid has a specific electrical conductance in the range of normal drinking water or greater, the immersed rod will decrease the resistance of the circuit and shunt out the meter signal to the CMD in many cases. The English rod also lacks any leveling device, and is placed in a vertical position using the hydrographers "best guess" only. This may allow the meter to be positioned out of vertical alignment with the flow streamline and cause a velocity reading error. Finally, the English rod is heavy, bulky and awkward, difficult to set up, and unwieldy to use. What is desired is a lightweight, durable, internally wired wading rod that isolates the electronic signal from the stream, and which can be used safely, accurately and conveniently as well.